Method And Apparatus For Mounting Semiconductor Chips

ABSTRACT

A method for mounting semiconductor chips onto a substrate with which substrate places are arranged in columns, whereby the semiconductor chips adhering to a foil are presented on a wafer table, whereby the detachment of a semiconductor chip from the foil is supported by means of a die ejector and whereby a pick and place device picks the semiconductor chip presented above the die ejector and deposits it onto the substrate comprises:
         Forward feeding the substrate along a transport direction designated as x direction,   Equipping a predetermined number of columns with semiconductor chips in accordance with the steps:   Moving the pick and place device to an x position corresponding to the column to be equipped,   Moving the die ejector to this x position, and   Equipping the substrate places of the column.

PRIORITY CLAIM

The present application is a divisional of U.S. patent application Ser.No. 11/173,396, filed Jul. 1, 2005, which claims priority under 35 U.S.C§ 119 based upon European Patent Application No. 04103158.4 filed onJul. 2, 2004.

FIELD OF THE INVENTION

The invention concerns a method and an apparatus for mountingsemiconductor chips onto a substrate.

BACKGROUND OF THE INVENTION

Different types of automatic assembly machines are known for mountingsemiconductor chips onto a substrate. At one end of the spectrum onefinds the so-called Die Bonders that are used in order to mountsemiconductor chips onto a substrate at high speed and with greataccuracy. Such Die Bonders are known for example from the patent U.S.Pat. No. 6,185,815, and the patent publications EP 991 11 0, US2005-0011067 and US 2004-0246794. The semiconductor chips are presentedon a wafer table. The substrates to be equipped are supplied one afterthe other in cycles whereby one substrate at a time is fixed to asubstrate table and presented for equipping with semiconductor chips.Mounting of the semiconductor chips is done by means of a bondheaddriven by a pick and place device. Die Bonders marketed by the applicantcontain a pick and place device with a first fast axis that enables thetransport of the semiconductor chips from the wafer table to thesubstrate at high speed and with a second axis running orthogonally tothe first axis that allows shifting of the semiconductor chip in therange of several tens of micrometers so that any deviation of the actualposition from the set position can be corrected. This concept enables asimple and favourable method of construction however limits the DieBonder to the effect that each time only one specific semiconductor chipcan be mounted onto the substrate. At the other end of the spectrum onefinds so-called automatic placement machines that have two fast axesrunning orthogonally to each other that cover a large working area. Theadvantage of this concept is that several different types ofsemiconductors as well as other components can be mounted one after theother onto the same substrate. The disadvantage is that the assemblytime is much greater than with a Die Bonder.

With the Die Bonder, the substrates are pushed forward in cycles by atransport device and, with substrates having several substrate placeslying next to each other in columns, are processed column by column. Thesubstrate is only pushed forward when a column is fully equipped withsemiconductor chips. There are also applications with which severalcolumns are combined into a block. Because the forward feed with thetransport device during equipping of a block for various reasons isoften undesired, Die Bonders have been developed with which thesubstrate table can be shifted in transport direction together with thesubstrate fixed to the substrate table so that the columns of a blockcan be equipped without having to release the fixing of the substrate tothe substrate table.

From U.S. Pat. No. 6,519,840 a semiconductor mounting apparatus is knownwith which the position of the semiconductor chip presented on the wafertable is measured by a camera before it is picked and a correction ofany positional deviation of the semiconductor chip from its set positionis done in that the foil is held by the die ejector by means of vacuumand then at least the upper surface of the die ejector facing towardsthe foil is shifted in the plane running parallel to the underside ofthe foil. The movement range of this die ejector is comparatively small,as it only has to enable small correction movements.

From U.S. Pat. No. 6,149,047 a semiconductor mounting apparatus is knownwith which the wafer table, the pick and place device and the dieejector can be moved in two horizontal directions so that thesemiconductor mounting apparatus has room in the smallest possible spacedespite the increasing size of the wafers. The disadvantage is thedistinct slowing down of the assembly process.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is to improve a Die Bonder in such a waythat several adjacent columns of substrate places can be processedwithout the substrate having to be pushed forward after processing eachcolumn and without the substrate table having to be moveable intransport direction.

The invention is based on the knowledge that in principle it is possibleto build a pick and place device with two fast axes with which both axescover a working area of several centimetres but that such a constructionbecomes very complex when both axes have to be moved for the equippingof each semiconductor chip. On the one hand, the invention thereforeproposes to equip the pick and place device with an axis runningparallel to the transport direction of the substrate that covers aworking area of several centimetres and, on the other hand, alsoequipping the die ejector that supports the detachment of thesemiconductor chips from the foil with a motorised axis running parallelto the transport direction of the substrate that covers the same workingarea. Once a column has been completely equipped with semiconductorchips and the next column is to be equipped with semiconductor chips,this construction enables moving both the pick and place device as wellas the die ejector parallel to the transport direction of the substrateso that several columns can be equipped without having to move thesubstrate and that during equipping of the substrate places that belongto the same column the bondhead only has to carry out possiblecorrection movements in the transport direction of the substrate thatare small in comparison with the distance between adjacent columns sothat a permanent back and forth movement of the bondhead overcomparatively large distances parallel to the transport direction of thesubstrate is omitted.

With this solution, the invention accepts an enlargement of thesemiconductor mounting apparatus as the pick and place device has atwo-dimensional working area. The movement range of the wafer table inthe transport direction of the substrate has to be enlarged by theworking area of the die ejector in order that the semiconductor chipssituated at the edge of the wafer can also be positioned above the dieejector in every possible position of the die ejector and picked up bythe bondhead of the pick and place device.

The invention therefore concerns a method for mounting semiconductorchips onto a substrate having at least two substrate places foraccepting semiconductor chips arranged next to each other in a column,whereby the semiconductor chips adhering to a foil are presented on awafer table, whereby the detachment of a semiconductor chip from thefoil is supported by means of a die ejector and whereby a pick and placedevice picks the semiconductor chip presented above the die ejector anddeposits it on the substrate place to be equipped. The method ischaracterised by the following steps:

Forward feeding the substrate along a transport direction designated asx direction,

Equipping a predetermined number of columns with semiconductor chips inaccordance with the steps:

Moving the pick and place device in the transport direction to an xposition corresponding to the column to be equipped,

Moving the die ejector to this x position,

Equipping the substrate places of the column with semiconductor chips inthat

a) the wafer table is moved in order to present the next semiconductorchip above the die ejector, and

b) the pick and place device picks the semiconductor chip presentedabove the die ejector and deposits it onto the substrate place to beequipped,

whereby steps a and b are repeated until all substrate places of thecolumn are equipped.

An apparatus for mounting semiconductor chips suitable for executingthis method comprises a rigidly arranged substrate table with a supportsurface for supporting a substrate, a transport device for transportingthe substrate along a predetermined transport direction, a wafer tablefor presenting a semiconductor chip, a die ejector for supportingdetachment of the semiconductor chip from the wafer table and a pick andplace device with a bondhead for picking the semiconductor chippresented above the die ejector and placing the picked semiconductorchip onto the substrate. The die ejector is moveable by a predetermineddistance d0 parallel to the transport direction of the substrate bymeans of a drive and the wafer table is moveable by a predetermineddistance DW=P+d0 parallel to the transport direction, whereby thequantity P designates the diameter of the largest wafer for theaccommodation of which the wafer table (and the apparatus) are designed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent invention and, together with the detailed description, serve toexplain the principles and implementations of the invention. The figuresare not to scale. In the drawings:

FIG. 1 shows a schematic plan view of a semiconductor mountingapparatus,

FIG. 2-4 show different snapshots during equipping of a substrate withsemiconductor chips that has substrate places arranged in columns.

DETAILED DESCRIPTION OF THE INVENTION

The invention concerns a semiconductor mounting apparatus that is knownin the trade as a Die Bonder. FIG. 1 shows a schematic plan view of sucha semiconductor mounting apparatus. The semiconductor mounting apparatuscomprises a rigidly arranged substrate table 1 with a support surfacefor the substrate 2, a transport device 3 for transporting the substrate2 along a predetermined transport direction designated as x direction, awafer table 4 with the semiconductor chips 5 to be mounted, a dieejector 6 to support detachment of the next semiconductor chip 5 to bemounted from the wafer table 4, a pick and place device 7 with abondhead 8 that picks the semiconductor chip presented above the dieejector 6 and places it onto the substrate 2, and a control device 9.The pick and place device 7 enables movements of the bondhead 8 alongtwo directions running orthogonally to each other designated as x and y.The pick and place device 7 contains a first, stationary arranged guide10 on which a first shuttle 11 bears that is moveable back and forth inx direction. The first shuttle 11 contains a second guide 12 on which asecond shuttle 13 bears that is moveable back and forth in y direction.The bondhead 8 is located on the second shuttle 13. Each of the twoshuttles 11 and 13 is driven by a drive 14 and 15. The two shuttles 11and 13 therefore enable movements of the bondhead 8 in x and ydirection. The die ejector 6 bears on a third guide 16 and is moveablein x direction, ie, parallel to the transport direction of the substrate2, by means of a further drive 17. From a middle position designated asx₀, the first shuttle 11 as well as the die ejector 6 can be moved backand forth in x direction within a predetermined working area [x₀-d,x+d]. The distance d amounts for example to 40 millimetres. Thetransport device 3 comprises for example a guide 18 for guiding at leastone moveable clamp 19. The transport device 3 transports the substrates2 one after the other to the bonding location where the pick and placedevice 7 deposits each semiconductor chip onto a respective substrateplace. In the figure, the four guides 10, 12, 16 and 18 are presentedsymbolically with arrows that illustrate the moving area of the shuttles11 and 13, the die ejector 6 as well as the clamp 19.

The semiconductor chips 5 adhere to a foil 20 clamped in a frame (knownin the trade as blue tape). The wafer table 4 accommodates the frame.With the semiconductor mounting apparatus in accordance with prior art,the die ejector 6 is arranged stationary. The wafer table 4 is moveableparallel and orthogonal to the transport direction of the substrate 2,ie, in x direction and in y direction, so that one semiconductor chip 5after the other can be positioned above the die ejector 6 from where itcan be picked by the bondhead 8 and mounted on the presented substrate2. The movement range D_(w) of the wafer table 4 in x direction has tobe enlarged by the distance d₀=2d whereby the distance d, as givenabove, characterises the working area [x₀-d, x₀+d] of the die ejector 6,so that, in every possible x position of the die ejector 6, thesemiconductor chips 5 situated at the edge of the wafer can also bepositioned above the die ejector 6 and picked up by the bondhead 8 ofthe pick and place device 7. The movement area D_(W) of the wafer table4 in x direction therefore amounts to P+d₀, whereby P designates thediameter of the largest wafer for acceptance of which the wafer table 4is designed or specified.

The control device 9 is arranged to synchronously move the pick andplace device 7 and the die ejector 6 parallel to the transport directionof the substrate 2 so that substrates with which at least two substrateplaces for accepting semiconductor chips are arranged next to each otherin a column can be equipped column by column with semiconductor chipswithout the bondhead 8 having to be moved parallel to the transportdirection of the substrate 2 except for comparatively small correctionmovements.

In order that the semiconductor chips 5 can be placed with greatpositional accuracy onto the substrate places, the position of thesemiconductor chip presented above the die ejector 6 and the position ofthe substrate place are measured with appropriate cameras and convertedinto motion signals for the pick and place device.

FIGS. 2 to 4 give a representative illustration of such a method formounting semiconductor chips onto a substrate with which four substrateplaces 21 for accepting semiconductor chips are arranged next to eachother in a column and with which three successive columns 22, 23 and 24form a block 25. Equipping of the substrate places of such a block 25takes place in accordance with the following process steps:

-   -   The substrate 2 is pushed forward in x direction by the        transport device 3 until the middle column 23 assumes the x        position x₀. The x position of the first column 22 is designated        as x₁, the x position of the third column 24 is designated as        x₂. The positions x₁ and x₂ result from the position x₀        corresponding to the distance D between two adjacent columns of        the block 25.    -   The pick and place device 7 is brought into the x position x₁ in        which its y axis is centred above the first column 22.    -   The die ejector 6 is also brought into the x position x₁.        This condition is presented in FIG. 2.    -   The substrate places 21 of the first column 22 are equipped one        after the other in that    -   a) the wafer table 4 is moved in order to present the next        semiconductor chip 5 above the die ejector 6, and        -   b) the pick and place device 7 picks the semiconductor chip            5 presented above the die ejector 6 and deposits it onto the            substrate place 21 to be equipped. With this process, the            bondhead 8 (FIG. 1) of the pick and place device 7 covers a            comparatively large distance in y direction. However, in x            direction the bondhead 8 only carries out a comparatively            small correction movement Δx in order to eliminate any wrong            positioning of the semiconductor chip. “Small” correction            movement means that Ax is very small in comparison with the            distance D between adjacent columns.

Steps a and b are repeated until all substrate places 21 of the firstcolumn 22 are equipped.

The middle column 23 is then equipped with semiconductor chips.Therefore, to equip the second, middle column 23,

-   -   the pick and place device 7 is brought into the x position x₀ in        which its y axis is centred above the middle column 23.    -   The die ejector 6 is brought into the x position x₀.        This condition is presented in FIG. 3.    -   The substrate places 21 of the middle column 23 are now equipped        one after the other in that a) the wafer table 4 is moved in        order to present the next semiconductor chip 5 above the die        ejector 6, and    -   b) the pick and place device 7 picks the semiconductor chip 5        presented above the die ejector 6 and deposits it onto the        substrate place to be equipped, whereby the bondhead 8 only        carries out a comparatively small correction movement in x        direction.

Steps a and b are repeated until all substrate places 21 of the middlecolumn 23 are equipped.

The third column 24 is then equipped with semiconductor chips.Therefore, to equip the third column 24,

-   -   the pick and place device 7 is brought into the x position x₂ in        which its y axis is centred above the third column 24.    -   The die ejector 6 is brought into the x position x₂.        This condition is presented in FIG. 4.    -   The substrate places 21 of the third column 24 are now equipped        one after the other in that        -   a) the wafer table 4 is moved in order to present the next            semiconductor chip 5 above the die ejector 6, and        -   b) the pick and place device 7 picks the semiconductor chip            5 presented above the die ejector 6 and deposits it onto the            substrate place to be equipped, whereby the bondhead 8 only            carries out a comparatively small correction movement in x            direction.

Steps a and b are repeated until all substrate places 21 of the thirdcolumn 24 are equipped.

All three columns 22, 23 and 24 of the same block 25 are now equipped.To equip the next block, the substrate 2 is now pushed forwardcorrespondingly by the transport device 3 until the middle column of thenext block assumes the position x₀. The three columns are then equippedwith semiconductor chips 5 as described above.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art having thebenefit of this disclosure that many more modifications than mentionedabove are possible without departing from the inventive concepts herein.The invention, therefore, is not to be restricted except in the spiritof the appended claims and their equivalents.

1. An apparatus for mounting semiconductor chips onto a substrate, theapparatus comprising a rigidly arranged substrate table with a supportsurface for supporting a substrate, a transport device for transportingthe substrate along a predetermined transport direction, a wafer tablefor presenting a semiconductor chip, a die ejector for supportingdetachment of the semiconductor chip from the wafer table, a Pick andPlace device with a bondhead for picking the semiconductor chippresented above the die ejector and placing the picked semiconductorchip onto the substrate, wherein the die ejector is moveable by apredetermined distance d₀ parallel to the transport direction of thesubstrate by means of a drive and wherein the wafer table is moveable bya predetermined distance D_(W)=P+d₀ parallel to the transport direction,whereby P designates a diameter of a largest wafer for the accommodationof which the wafer table is designed.